The first quasar to be discovered, 3C273, hosts a prominent and narrow jet of relativistic particles emitted from its galactic core. Detailed pictures of the jet show that it glows from radio to x-ray frequencies and, unusually, can even be seen in visible light. Physical models of the jet have tried to explain how it forms and retains its tight columnar shape despite traveling far beyond its parent galaxy.
Uchiyama et al. have examined mid-infrared images acquired with the Spitzer Space Telescope and find that the jet changes color abruptly in the middle. They attribute the long-wavelength (radio to infrared) radiation from the outer part of the jet to the synchrotron emission of charged particles moving at relativistic speeds along the jet in a strong magnetic field. In contrast, the inner part appears to be dominated by a high-energy component that exudes both x-rays and visible light. This short-wavelength emission could arise either from synchrotron radiation by a second population of electrons or protons--an explanation supported by current polarization data--or else from inverse Compton scattering of photons by jet particles. This result runs counter to prior theories that tied the origin of the optical light to the radio emission mechanism, and it suggests that optical emission may yet be detected in quasars with x-ray jets. -- JB
Astrophys. J. astro-ph/0605530 (2006).
